SM5964B
8-Bit Micro-controller
64KB with ISP Flash
& 1KB RAM embedded
9. Interrupt
The SM5964B provides 7 interrupt sources with two priority levels. Each source has its own request flag(s) located
in a special function register. Each interrupt requested by the corresponding flag could individually be enabled or
disabled by the enable bits in SFR’s IE.
When the interrupt occurs, the engine will vector to the predetermined address as given in Table 9-1. Once
interrupt service has begun, it can be interrupted only by a higher priority interrupt. The interrupt service is
terminated by a return from instruction RETI. When an RETI is performed, the processor will return to the
instruction that would have been next when interrupt occurred.
When the interrupt condition occurs, the processor will also indicate this by setting a flag bit. This bit is set
regardless of whether the interrupt is enabled or disabled. Each interrupt flag is sampled once per machine cycle,
and then samples are polled by hardware. If the sample indicates a pending interrupt when the interrupt is enabled,
then interrupt request flag is set. On the next instruction cycle the interrupt will be acknowledged by hardware
forcing an LCALL to appropriate vector address.
Interrupt response will require a varying amount of time depending on the state of microcontroller when the
interrupt occurs. If microcontroller is performing an interrupt service with equal or greater priority, the new interrupt
will not be invoked. In other cases, the response time depends on current instruction.
Table 9-1: Interrupt vectors
Priority
level
Interrupt Vector
Address
Interrupt Number
*(use Keil C Tool)
Interrupt Request Flags
1 (highest)
IE0 – External interrupt 0
TF0 – Timer 0 interrupt
0003h
000Bh
0013h
001Bh
0023h
002Bh
003Bh
0
1
2
3
4
5
7
2
3
4
5
6
7
IE1 – External interrupt 1
TF1 – Timer 1 interrupt
RI/TI – Serial channel interrupt
TF2/EXF2 – Timer 2 interrupt
Two Wire Serial Interface
*See Keil C about C51 User’s Guide about Interrupt Function description
Mnemonic
Description
Dir.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
RST
Interrupt
Interrupt Enable
Register
Interrupt Enable
Register 1
Interrupt Priority
Register
Interrupt Priority
Register 1
IE
IE1
IP
A8H
A9H
B8H
B9H
EA
-
-
-
-
ET2
ES
-
ET1
EX1
ET0
ETWSI
PT0
EX0
00H
00H
00H
00H
-
-
-
-
PT2
-
-
PT1
-
-
PX1
-
-
PX0
-
PS
-
IP1
PTWSI
Mnemonic: IE
Address: A8h
7
6
5
4
3
2
1
0
Reset
EA
-
ET2
ES
ET1
EX1
ET0
EX0
00h
EA: EA=0 – Disable all interrupt.
EA=1 – Enable all interrupt.
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M081 Ver A SM5964B 3/7/2014
- 38 -
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
